TV Sound transmission system

ABSTRACT

A television signal audio transmission system comprises transmission means for developing first and second stereophonically related audio signals and means for developing a third audio signal. The transmission means further includes circuitry for developing a composite baseband signal having a first component comprising the sum of the first and second audio signals, a second component comprising a double sideband suppressed carrier signal formed by amplitude modulating a 2f H  subcarrier with the difference between the first and second audio signals, a third component comprising a pilot signal having a frequency f H  and a fourth component comprising a 4f H  subcarrier signal frequency modulated according to the third audio signal, where f H  represents the horizontal scanning line frequency. The composite baseband signal may include a fifth component comprising an approximately 5.5f H  subcarrier signal frequency modulated in accordance with a first information signal and a sixth component comprising an approximately 6.5f H  subcarrier signal frequency modulated in accordance with a second information signal. In an alternate embodiment, the fourth and fifth components are replaced by a 5f H  subcarrier signal frequency modulated according to the third audio signal. The composite baseband signal is used to frequency modulate a transmitted main audio RF carrier, the transmitted signal being detected by receiving circuits for reproducing the stereophonic audio signals, the third audio signal and the first and second information signals.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of co-pending application Ser. No.196,491, filed Oct. 14, 1980 now U.S. Pat. No. 4,339,772. Thisapplication contains new matter primarily in the Abstract, in FIGS. 10and 11 of the drawings.

BACKGROUND OF THE INVENTION

The present invention relates generally to a new and improved televisionaudio transmission system and is particularly directed to apparatus andmethods for transmitting and receiving an audio signal which iscompatible with existing television audio receiving circuits and whichcomprises a series of components, including stereophonic components,efficiently utilizing the audio bandwidth of a broadcast televisionchannel.

Under present television broadcasting standards, a band of frequenciesapproximately 80 KHz wide is designated within each 6 MHz televisionchannel for the transmission of the audio component of a televisionsignal. Within this band of frequencies, an RF main audio carrier signalis frequency modulated by an audio baseband signal for producing amonaural audio transmission signal. The transmitted monaural audiosignal is received by a television receiver which converts the RF audiocarrier signal to a signal having a frequency centered at 4.5 MHz. Theconverted 4.5 MHz sound carrier is then processed by an FM detector toreproduce the monaural audio signal which was used to frequency modulatethe RF audio carrier at the transmitter. In this regard, it has beenrecognized that the audio bandwidth of a television channel hasheretofore been largely underutilized whereby the opportunity totransmit a substantial amount of information in addition to theconventional monaural signal over this frequency band has not been takenadvantage of. It is accordingly a basic object of the present inventionto provide a system more fully exercising the audio bandwidth of aconventional television channel and which is compatible with present-daytelevision receivers. More particularly, it is an object of the presentinvention to provide apparatus for transmitting and receivinginformation over the audio bandwidth of a television channel whichinformation includes stereophonic sound components as well as a numberof additional audio information components.

The transmission of stereophonic audio signals has been popular in radiobroadcasting for some time, the basic FCC approved system beingdisclosed in U.S. Pat. No. 3,257,511 to R. Adler et al. In this system,the arithmetic sum of left (L) and right (R) audio source signals (L+R),commonly referred to as the main channel modulation, is used to directlyfrequency modulate the RF carrier signal. The difference between theleft and right stereophonically related signals (L-R) is used toamplitude modulate a 38 KHz subcarrier signal in a suppressed carrierfashion with the resultant double-sideband signal being impressed asfrequency modulation on the radiated RF carrier. In addition, a pilotsubcarrier signal of 19 KHz is transmitted for synchronization of the FMreceiver. The FM receiver extracts the 19 KHz pilot subcarrier, doublesits frequency, and applies the resulting 38 KHz signal to a synchronousdetector where the (L-R) difference signal is recovered from theamplitude modulated 38 KHz stereophonic subcarrier. The recovered (L-R)modulation is then suitably matrixed with the (L+R) main channelmodulation in order to recover the original left and right stereophonicsignals.

The foregoing stereophonic radio broadcasting system often also includesan SCA component which allows broadcasters to provide a subscriptionbackground music service. The SCA component comprises a 67 KHzsubcarrier frequency modulated by the background channel program, thefrequency modulated subcarrier being used to frequency modulate the mainRF carrier signal together with the stereophonic modulation.

Various systems and apparatus have been proposed for the transmission ofstereophonic sound together with a conventional television picturetransmission. These systems normally utilize the radio broadcastingstereophonic transmission techniques discussed above but with, in mostcases, different subcarrier frequencies selected for their compatibilitywith the transmitted video signal. One such prior art system isdisclosed in U.S. Pat. No. 4,048,654 to Wegner. This patent discloses atransmission system in which a composite baseband signal identical tothat employed in FM stereophonic radio broadcasting is employed tofrequency modulate the main sound carrier of a television transmissionsignal. Thus, the proposed composite baseband signal includes an (L+R)main channel component, an amplitude modulated double-sidebandsuppressed-carrier 38 KHz subcarrier (L-R) component and a 19 KHz pilotcomponent. In another embodiment, the use of a subcarrier signal havinga frequency equal to 5/4 of the horizontal scanning line frequency(f_(H)) characterizing the transmitted video signal is proposed in lieuof the 38 KHz (L-R) channel subcarrier to reduce interference from thevideo component of the television signal.

Another system, which was proposed in U.S. Pat. No. 3,099,707 to R. B.Dome, also employed the conventional stereophonic radio broadcastingsystem but with an (L-R) channel subcarrier equal to 1.5f_(H) and apilot signal equal to 2.5f_(H). These frequencies were selected tominimize the effect of the video components of the television signalappearing in the recovered sidebands of the (L-R) channel signal.

U.S. Pat. No. 3,046,329 to Reesor discloses yet another similar systemin which the composite baseband signal used to frequency modulate themain sound carrier includes only the main channel (L+R) component andthe upper sidebands of the (L-R) channel signal amplitude modulated on asubcarrier having a frequency of 2f_(H). Other prior art systems forstereophonic television sound transmission have proposed the use offrequency modulated subcarriers for the (L-R) stereo channel typicallycentered at 2f_(H) although a center frequency of 1.5f_(H) has also beenproposed.

As previously mentioned, in addition to transmitting stereophonic soundcomponents on the main aural carrier of a transmitted television signal,it is also desirable to transmit additional information thereby morecompletely exercising the available audio bandwidth within a televisionchannel. For example, the transmission of a second language audio signalwould enable a viewer to selectively operate a television receiver forreproducing the audio signals associated with the transmittedstereophonic information, or alternatively, the audio signals associatedwith the transmitted second language information. Other examples of suchadditional information include ENG electronic news gathering) signalsand telemetry signals, both of which television broadcasters employ fortheir own private use. ENG signals are employed to provide a directcommunications link between a broadcasters and his station's remotecamera crews for real-time news reporting while telemetry signalsconsist of FCC required remote read-outs from unattended transmitterlocations to a control location.

One prior art proposal for providing a second language capability inconnection with a transmitted television signal is disclosed inpreviously mentioned U.S. Pat. No. 4,048,654 to Wegner in which the twochannels of a stereophonic-like signal are employed. In particular, the(L+R) main channel signal is used to transmit a first language audiosignal and the (L-R) stereo channel signal is used to transmit a secondlanguage audio signal. U.S. Pat. No. 3,221,098 to Feldman discloses atransmission system allowing for the simultaneous broadcast of a singletelevision program having up to four or more different languagesoundtracks by forming a composite baseband signal consisting of four ormore different subcarrier signals each amplitude modulated with adifferent language audio signal, the composite baseband signal beingused to frequency modulate the main RF audio carrier. Yet anotherproposed second language system uses a frequency modulated subcarrierbaseband signal centered at 2f_(H) for both stereophonic soundtransmission and for second language transmission. A pilot signal,modulated with one of two different frequencies, is used to indicatewhich service is being broadcast.

The foregoing systems and techniques for transmitting different audiosignals in conjunction with a standard television transmission have notbeen adopted in the U.S. for a number of reasons including, in certaincases, poor performance and, in others, incompatibility with U.S.television transmission standards. The system of the present invention,on the other hand, comprises a audio transmission system which is fullycompatible with U.S. television broadcasting standards and is capable ofproviding high-fidelity stereophonic sound transmissions together with ahigh quality second language service. The system is furthercharacterized in that ENG and telemetry signals are also convenientlyaccommodated within the audio bandwidth of a television channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a television signal transmitterincluding apparatus for transmitting both the video and audio componentsof a television signal.

FIG. 2 is a functional block diagram illustrating the preferredembodiment of a composite baseband signal source constructed accordingto the present invention useful for frequency modulating the main audioRF carrier signal produced by the carrier oscillator of FIG. 1.

FIG. 3 is a graphic representation of the frequency spectrum of thecomposite baseband signal developed by the signal source of FIG. 2.

FIG. 4 is a functional block diagram of the portions of a televisionreceiver adapted for reproducing the audio stereophonic components ofthe composite baseband signal illustrated in FIG. 3.

FIG. 5 is a functional block diagram illustrating a preferred embodimentof the 2f_(H) subcarrier regenerator shown in FIG. 4.

FIGS. 6A and 6B are functional block diagrams illustrating two alternateembodiments of the stereo decoder of FIG. 4.

FIG. 7 is a functional block diagram of the portions of a televisionreceiver adapted for selectively reproducing either the stereophonic orthe second language audio components of the composite baseband signalshown in FIG. 3.

FIG. 8 is a functional block diagram of a receiver adapted forreproducing the ENG component of the composite baseband signal of FIG.3.

FIG. 9 is a functional block diagram of a receiver adapted forreproducing the telemetry component of the composite baseband signal ofFIG. 3.

FIG. 10 is a graphic representation of the frequency spectrum of analternate composite baseband signal according to the invention.

FIG. 11 is a functional block diagram illustrating a composite basebandsignal source adapted for producing the composite baseband signal shownin FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and, in particular, to FIG. 1, aconventional television signal transmitter is shown to comprise a videochannel 10 and an audio channel 20. The video channel 10 includes asource of video signals 12, a sync generator 14 connected to the videosource 12 and an RF carrier oscillator 16, the oscillator 16 and thevideo source 12 supplying a video modulator 18. The video modulator 18develops an output signal comprising a continuous sequence of horizontalscanning lines defined by the sync generator 14, each horizontalscanning line consisting of the RF carrier developed at the output ofthe carrier oscillator 16 amplitude modulated by the output of the videosource 12. According to FCC standards, the horizontal scanning linefrequency f_(H) is approximately 15.75 KHz. The output of the videomodulator 18 is amplified by a power amplifier 19 and coupled through aconventional diplexer 30 and transmitted via an antenna 32.

The aural channel 20 of the transmitter shown in FIG. 1 conventionallyincludes a source of monaural audio signals 22 and an RF carrieroscillator 24 both supplying an audio modulator 26. The output of theaudio modulator 26, which consists of the RF carrier developed at theoutput of the oscillator 24 frequency modulated by the output of theaudio source 22, is amplified by a power amplifier 28 and coupledtherefrom through the diplexer 30 for transmission via the antenna 32.As discussed previously, the audio source 22 conventionally develops amonaural signal for transmission by the aural channel 20 of thetelevision signal transmitter. As will be explained in detailhereinafter, it is a primary object of the present invention to morecompletely exercise the aural channel 20 by impressing thereon astereophonic audio signal together with a corresponding second languageaudio signal. In addition, the invention further discloses a techniqueby which an ENG signal and a telemetry signal may also be impressed onthe audio channel 20.

FIG. 2 illustrates a portion of the aural channel of a television signaltransmitter constructed according to the invention disclosed in thereferent co-pending parent application. The circuit illustrated in FIG.2 which, in terms of the transmitter of FIG. 1, is represented by theaudio source 22, develops an output composite baseband signal having aspectrum as graphically represented in FIG. 3. This composite basebandsignal is used to frequency modulate the main aural carrier signaldeveloped by the carrier oscillator circuit 24 and is coupled from theaural modulator 26 through the power amplifier 28 and the diplexer 30for transmission by the antenna 32.

Referring now in detail to FIG. 2, the audio channel is seen to comprisea first audio source 34 and a second audio source 36 for developing apair of stereophonically related audio signals L (left) and R (right)respectively. Audio sources 34 and 36 may comprise, for example,microphones, pickup circuits of a record player capable of reproducing astereo recording or any other similar source of stereophonic audiosignals. The outputs of the audio sources 34 and 36 are coupled to apair of 75 microsecond pre-emphasis networks 38 and 40 which, in a wellknown manner, emphasize the high frequency components of the audiosignals relative to the low frequency components thereof so as toachieve certain noise advantages. The outputs of the pre-emphasisnetworks 38 and 40 are coupled through a pair of 15 KHz low pass filters39 and 41, respectively, to the inputs of a pair of notch filters 42 and44. The notch filters 42 and 44 have frequency response characteristicscentered at the horizontal scanning line frequency f_(H) for removingany audio components from the signals L and R near the frequency f_(H)and couple the filtered and emphasized audio signals to a stereo encoder46.

The stereo encoder 46, as is well known in the art, may use either timeor frequency division multiplexing techniques for developing a mainchannel audio signal on a first output line 48 and a stereo subchannelsignal on a second output line 50. More specifically, the main channelaudio signal, which is limited to a bandwidth of 15 KHz by the low passfilters 39 and 41, comprises the arithmetic sum of the left and rightstereophonic audio source signals (L+R) and is formed on the output line48 by an addition process performed by the adder circuit 52. The stereosubchannel signal developed on output line 50 is formed by using thedifference between the left and right stereophonic source signals (L-R),this difference signal being developed at the output of a blockrepresented by a subtractor circuit 54, to amplitude modulate asubcarrier signal having a frequency 2f_(H) in a balanced modulator 56for producing a double sideband suppressed-carrier signal. The 2f_(H)subcarrier signal is coupled to the modulator circuit 56 by a subcarrierand a pilot generator 58 which comprises a phase lock circuit for phaselocking the 2f_(H) subcarrier signal to the second harmonic of thetelevision signal horizontal sync pulses developed by the sync generator14. The use of the 2f_(H) subcarrier for the stereo subchannel signalavoids the production of audible beats with the horizontal scanning linefrequency while, at the same time, allowing for a 15 KHz audiobandwidth. The subcarrier and pilot generator 58 also develops a pilotsignal on an output line 60 having a frequency f_(H).

The main channel audio signal developed on line 48, the stereosubchannel signal developed on line 50 and the pilot signal developed online 60 are all coupled by a summation circuit 62 through a 47 KHzlinear phase low pass filter 64 to the first input 66 of a secondsummation circuit 68, the output of summation circuit 68 correspondingto the output of the audio source 22 of FIG. 1. That is, the compositebaseband signal developed at the output of summation circuit 68 is usedto frequency modulate the main RF audio carrier in the modulator 26.With reference to FIG. 3, the components of the composite basebandsignal coupled to the input 66 of the summation circuit 68 thereforeinclude the 15 KHz bandwidth (L+R) main channel signal, the pilot signalat frequency f_(H) and the 15 KHz bandwidth upper and lower sidebands ofthe stereo subchannel signal.

As mentioned above, the composite baseband signal developed at theoutput of summation circuit 68 is used to frequency modulate the main RFaural carrier signal developed by oscillator 24. While the maximum mainaural carrier frequency deviation due to either the main channel signalor the stereo subchannel signal is limited to 25 KHz, in accordance withthe well known interleaving phenomenon characteristic of these signals,the total maximum main carrier frequency deviation in response to bothsignals is limited to a total of 25 KHz. The main carrier frequencydeviation due to the pilot signal is 2.5 KHz so that the total maincarrier frequency deviation due to the components of the compositebaseband signal coupled to the input 66 of summation circuit 68 amountsto 27.5 KHz.

The circuit of FIG. 2 includes a third source of audio signals 70supplying, for example, a second language audio signal, it beingintended that a viewer's television receiver is operable for selectivelyreproducing either the stereophonic signal described above or the secondlanguage audio signal. The second language source 70 is coupled througha pre-emphasis circuit 72 and a 12 KHz low pass filter 74 to one inputof an FM modulator 76. The 12 KHz audio bandwidth established by filter74 is considered sufficient to allow better quality than is needed forthe processing of speech-type audio signals alone, such comprising thenormal content of the audio signal developed by the source 70 therebyalso allowing for the processing of some types of audio music signals.Although not shown in the drawings, this channel may incorporatecompanding techniques, e.g. of the Dolby or DBX type, to further enhancethe reproduction qualities of the second language signal.

The subcarrier and pilot generator 58 couples a subcarrier signal phaselocked to 4f_(H) to the second input of the FM modulator 76. As aconsequence, the FM modulator 76 develops an output signal consisting ofthe 4f_(H) subcarrier signal frequency modulated by the second languageaudio signal. It will be appreciated that centering this signal at aharmonic of the horizontal scanning line frequency f_(H) effectivelyinhibits the generation of audible inter-modulation in the reproductionaudio signal. The frequency modulated 4f_(H) subcarrier signal is bandpass filtered by filter 78 and coupled to the second input 80 of thesummation circuit 68. The frequency characteristics of the bandpassfilter 78 and the extent of the frequency deviation of the main auralcarrier due to the frequency modulated second language audio signal areselected so as to limit the bandwidth of the frequency modulated secondlanguage audio signal for preventing interference with adjacentchannels. With reference to FIG. 3, the second language audio componentof the composite baseband signal developed at the output of thesummation circuit 68 is therefore seen to comprise a 4f_(H) subcarriertogether with its associated upper and lower FM sidebands extendingapproximately 12 KHz above and below 4f_(H) respectively.

The circuit of FIG. 2 further includes a source of ENG (electronic newsgathering) signals 82 and a source of telemetry signals 84. The ENGsignals, which allow a broadcaster to directly communicate with thestation's camera crews in the field for real-time news reports and thelike, are coupled through a 150 microsecond pre-emphasis circuit 86 tothe input of a 3.4 KHz low pass filter 88. The resulting 3.4 KHzbandwidth signal is impressed as a frequency modulation on anapproximately 5.5f_(H) subcarrier signal by a second FM modulator 90 andcoupled therefrom through a bandpass filter 92 to a third input 94 ofthe summation circuit 68. The telemetry signals developed by the source84, which consist of transmissions from unattended transmitterlocations, are band limited by a 2 KHz low pass filter 96 andsubsequently impressed as frequently modulation on an approximately6.5f_(H) subcarrier signal by a third FM modulator 98. The frequencymodulated 6.5f_(H) subcarrier signal is coupled from the modulatorthrough a bandpass filter 100 to a fourth and final input 102 of thesummation circuit 68. The FM modulated ENG and telemetry signals areeffective for causing maximum main aural carrier frequency deviations of4.0 and 1.25 KHz respectively.

Typical stereo demodulators are operative for demodulating a transmittedstereophonic signal at odd harmonics of the stereo subcarrier frequency.As discussed above, the subcarrier signal used to form the stereosubchannel signal in the circuit of FIG. 2 is characterized by afrequency of 2f_(H), the third harmonic of which is equal to 6f_(H). Theuse of a subcarrier having a frequency of 6f_(H) for either the ENGsignals or the telemetry signals would therefore cause interference withthe stereo subchannel signal. Accordingly, the subcarriers selected foruse with these signals have been displaced about 0.5f_(H) above andbelow the third harmonic of the stereo subchannel subcarrier signal2f_(H).

It will thus be seen that the particular four subcarriers selected foruse in the circuit of FIG. 2 allow for the most efficient use of theaudio bandwidth associated with a transmitted television signal. Inparticular, referring to FIG. 3, it will be observed that, consideringthe 15 KHz bandwidth of the main channel (L+R) signal and the 15 KHzbandwidth of the lower sidebands of the stereo subchannel signal, thelowest harmonic of the horizontal scanning line frequency f_(H)available for use as the stereo subchannel subcarrier is 2f_(H). Asmentioned previously, it is desirable to use a harmonic of thehorizontal scanning line frequency f_(H) for this subcarrier in order toprevent the production of audible inter-modulation beats therebetween.Similarly, it is also desirable to use a harmonic of the horizontalscanning line frequency f_(H) as the subcarrier for the second languageaudio signal. Considering the 15 KHz bandwidth of the upper sidebands ofthe stereo subchannel signal and the approximately 12 KHz bandwidth ofthe second language signal, the next harmonic of the horizontal scanningline frequency f_(H) available for use as the second language subcarriersignal if 4f_(H). Allowing for sufficient separation between the uppersidebands of the frequency modulated second language signal and thelower sidebands of the frequency modulated ENG signal, the nextavailable harmonic of the horizontal scanning line frequency f_(H) is6f_(H). However, since 6f_(H) is an odd harmonic of the stereosubchannel subcarrier 2f_(H), its use as a subcarrier is not desirable.Consequently, subcarriers for the ENG and telemetry signals are spacedabout 0.5f_(H) therefrom at approximately 5.5f_(H) and 6.5f_(H). Themain carrier deviations and associated filter bandpass characteristicsfor these signals are so chosen to prevent interference with adjacentchannels. Any resulting beating of the subcarriers with the horizontalscanning line frequency is expected to be minimal.

The foregoing subcarriers together with other pertinent data describingthe operation of the circuit of FIG. 2 is presented in tabular formbelow:

                                      TABLE I                                     __________________________________________________________________________    Modulating Signal                                                                         L + R                                                                             Pilot                                                                            L - R                                                                              2nd language                                                                         ENG Telemetry                                  __________________________________________________________________________    Subcarrier Modulation                                                                     --  CW AM   FM     FM  FM                                                            DSB-SC                                                     Subcarrier Frequency                                                                      --  f.sub.H                                                                          2 f.sub.H                                                                          4 f.sub.H                                                                            5.5 f.sub.H                                                                       6.5 f.sub.H                                (KHz)                                                                         Subcarrier Deviation                                                                      --  -- --    8     3.5 3.0                                        (KHz)                                                                         Max. Subcarrier                                                                           15  -- 15   12     3.4 2.0                                        Modulating Frequency                                                          (KHz)                                                                         Pre-emphasis                                                                              75  -- 75   75     150 0                                          (microseconds)                                                                Main Carrier Deviation                                                                    25  2.5                                                                              25   15      4   1.25                                      (KHz)                                                                         __________________________________________________________________________

To summarize the foregoing, the composite baseband signal or compositemodulation function produced at the output of the summation circuit 68and impressed as frequency modulation on the main aural RF carrier bymodulator 26 comprises a series of distinct components. The initialmodulation function component comprises the 15 KHz main channel stereosignal (L+R) while the second component comprises the double-sidebandsuppressed carrier amplitude modulated stereo subchannel signal.Together these two components account for a frequency deviation of themain aural carrier of 25 KHz. The third modulation function componentcomprises a pilot signal having a frequency of f_(H) and accounts for anadditional 2.5 KHz of frequency deviation of the frequency modulatedmain aural carrier. The fourth modulation function component comprisesthe upper and lower sidebands together with the 4f_(H) subcarrier of thefrequency modulated second language audio signal. This FM signalprovides another 15 KHz of main carrier frequency deviation. The fifthand sixth modulation function components comprise the upper and lowersidebands and the 5.5f_(H) and 6.5f_(H) subcarriers associated with theENG and telemetry signals which account for a final contribution of 4.0and 1.25 KHz respectively to the main carrier frequency deviation. Thetotal main carrier frequency deviation due to the composite basebandsignal is therefore 47.75 KHz.

While the foregoing discussion indicates that the 5.5f_(H) and 6.5f_(H)subcarriers are used for transmitting ENG and telemetry signals, thisshould not be considered as a necessary limitation since thesesubcarrier signals may be used to transmit various other types ofinformation such as audio signals. In the case where the 5.5f_(H) and6.5f_(H) subcarriers are used to transmit audio signals, the parametersof Table I are preferably modified as follows:

                  TABLE II                                                        ______________________________________                                        Subcarrier Frequency (KHz)                                                                         5.5 f.sub.H                                                                           6.5 f.sub.H                                      Subcarrier Deviation (KHz)                                                                         5.0     5.0                                              Max Subcarrier       6.0     6.0                                              Modulating Frequency (KHz)                                                    Pre-Emphasis (microseconds)                                                                        150     150                                              Main Carrier Deviation (KHz)                                                                       3.0     3.0                                              ______________________________________                                    

FIG. 4 illustrates a television receiver constructed for reproducing thestereophonic sound transmissions characterizing the frequency modulatedmain aural RF carrier developed at the output of transmitting antenna32. The receiver includes an antenna 110 for intercepting thetransmitted RF signals, including both visual and aural components,which signals are coupled to a conventional television tuner 112. Thetuner 112 converts the received RF signals to corresponding intermediatefrequency (IF) signals which are amplified by an IF amplifier 114. Thevisual components of the amplified IF signal are coupled to a videodetector and therefrom to the remaining video processing circuits of thetelevision receiver while the inter-carrier components of the amplifiedIF signal are applied to a conventional FM detector stage 116. The FMdetector stage 116 functions in a manner well known in the art todemodulate the inter-carrier signal for recreating the compositebaseband signal on output conductor 118. The composite baseband signaldeveloped an conductor 118 is applied to one input of a conventionalstereo decoder network 120 which receives a second input from asubcarrier regenerator network 222. The f_(H) pilot signal developed onconductor 118 is coupled to an input of the regenerator network 122which develops an output in response thereto comprising a regenerated2f_(H) subcarrier signal phase locked to the pilot signal.Alternatively, the regenerator circuit 122 may operate in response tothe horizontal sync signal developed in the horizontal deflection stageof the receiver, as indicated by dotted line 124, for developingtherefrom the 2f_(H) regenerated subcarrier signal. In either case, thestereo decoder network 120 is responsive to the regenerated 2f_(H)subcarrier signal and to the main channel and stereo subchannel signalsfor developing emphasized representations of the left (L) and right (R)stereophonically related audio signals on a pair of output conductors126 and 128 respectively. These signals are de-emphasized by de-emphasiscircuits 130 and 132 to form accurate reproductions of the left (L) andright (R) stereophonically related audio signals which are coupled toseparate speaker systems 134 and 136 through amplifiers 135 and 137 forconversion to corresponding audio sounds.

The 2f_(H) subcarrier regenerator 122 of FIG. 4 may be of theconventional voltage controlled oscillator type but, preferably,comprises a phase-locked filter circuit of the type shown in FIG. 5. Theadvantage of this circuit is that the loop bandwidth can be madeextremely small for rejecting audio components of a signal frequencyclose to the pilot frequency. The bandwidth of a voltage controlledoscillator phase-locked loop cannot be made this small due to frequencypull-in considerations.

Referring to FIG. 5, the horizontal sync pulses developed on line 124are converted to a corresponding sine wave signal by a pulse to sinewave converter circuit 141 and coupled therefrom to the signal input ofa voltage controlled phase shifter 143. The control input of the voltagecontrolled phase shifter 143 is derived from the output of a low-passfilter 145 whose cut-off frequency determines the loop bandwidth. Theoutput of the voltage controlled phase shifter 143 is quadrature phaseshifted by a phase shift circuit 147 and coupled to the first input of aphase detector 149, the second input of the phase detector 149comprising the f_(H) pilot signal developed on line 118. The phasedetector 149 develops an output error signal which is coupled throughthe low-pass filter 145 to the control input of the voltage controlledphase shifter 143 for equalizing the phase of its output with the phaseof the f_(H) pilot signal. The output of the phase shifter 143accordingly comprises an extremely pure f_(H) sinewave signal phaselocked to the f_(H) pilot signal and therefore ideally suited for, afterbeing doubled in frequency by a frequency doubler circuit 151, operatingthe stereo decoder 120.

FIGS. 6A and 6B generally illustrate two alternate embodiments of thestereo decoder circuit shown in FIG. 4. The embodiment of FIG. 6Autilizes time division multiplexing techniques and is preferred in thesystem of the invention while the embodiment of FIG. 6B utilizesfrequency division multiplexing techniques. Referring specifically toFIG. 6A, the f_(H) pilot signal together with the horizontal sync pulsesare coupled to the 2f_(H) subcarrier regenerator 122, which preferablycomprises the phase-locked loop filter circuit of FIG. 5, forsynchronizing the operation thereof while the (L-R) sideband signals arecoupled to the input of a conventional switching demodulator 140. As iswell known in the art, the switching demodulator 140 is operative foreffectively multiplying the (L-R) sideband signals by a 2f_(H) squarewave signal represented by the output of a regenerator 122 to form anoutput signal which may be represented by the expression (L-R)+π/4(L+R).The latter signal together with the (L+R) main channel signal areapplied to the two inputs of a matrix 142 which suitably processes thesignals for developing the separate emphasized left (L) and right (R)audio signals on conductors 126 and 128 respectively. A particularadvantage is achieved using the foregoing time division demultiplexingtechnique in that the Fourier expansion of the square wave signal usedto operate the switching demodulator 140 includes odd order terms only.As a consequence, the 4f_(H) term is zero and none of the secondlanguage audio signal will therefore appear in the output of thedemodulator 140.

FIG. 6B illustrates the frequency division demultiplexing technique. Inthis case a doubly balanced demodulator 140' is used to develop an (L-R)signal which has no (L+R) component. The (L-R) signal developed at theoutput of demodulator 140' is suitably combined with the (L+R) mainchannel signal in a matrix 142' to develop the left (L) and right (R)signals on conductors 126 and 128.

In connection with the above, it is important to note that aconventional monaural television receiver tuned to a program broadcaststereophonically according to the above transmission system will receivein its audio channel the (L+R) audio signal which will provide aperfectly satisfactory signal to listen to. On the other hand, atelevision receiver including a stereophonic sound reproduction systemas shown in FIG. 4 and tuned to receive a monaural broadcast willproduce the monaural sound in its (L+R) channel but will not produce the(L-R) audio signal due to the absence of the (L-R) sidebands. In thiscase, both speakers 134 and 136 will be fed the (L+R) audio signal forreproducing the monaural sound in a perfectly satisfactory manner.

FIG. 7 illustrates a modification of the circuit of FIG. 4 whereby theviewer of a television receiver may select either the transmittedstereophonic signals or, alternatively, the second language audio signalfor reproduction. In this modification, the stereo decoder 120, the2f_(H) subcarrier regenerator 122 and the de-emphasis circuits 130 and132 are connected as shown in FIG. 4. The line 118, however, downstreamof the take-off point for the f_(H) pilot signal includes a seriallyconnected switch 144 ganged for operation together with a pair ofswitches 158 and 160 in response to a mute control circuit 146. Thecircuit further includes a bandpass filter 148 passing the secondlanguage component of the composite baseband signal to an FM subcarrierdetector 150. The output of the bandpass filter 148 is also coupled to amute drive circuit 152 which detects the presence of an FM subcarriersignal. The output of the mute drive circuit 152 is connected to a mutecontrol circuit 146 by a viewer operable selector switch 154. The outputof the FM detector 150 is coupled by a de-emphasis circuit 156 to theinputs of switches 158 and 160 whose outputs are connected to thespeakers 136 and 134 respectively. While the switches 144, 158 and 160are schematically illustrated as mechanical in nature, it is preferredthat these switches be implemented in an electronic form. Thus, forexample, each of the switches 144, 158 and 160 may comprise a transistorswitch operable in reponse to suitable output signals from the mutecircuit 146.

In operation, when the viewer selector switch 154 is in the positionshown in FIG. 7, no drive signal can be supplied to the mute circuit 146and the switches 144, 158 and 160 assume the positions shown in theFigure. In this condition of the circuit the stereo decoder 120 isoperative for energizing the speakers 134 and 136 through thede-emphasis circuits 130 and 132 for producing the separate stereophonicsignals as described above. However, when the viewer selector switch 154is moved to its closed position, the drive circuit 152, in response tothe presence of a second language subcarrier signal, energizes mutecircuit 146 which causes switch 144 to open and switches 158 and 160 toclose. The stereo decoder 120 is thereby decoupled from the FM detector116 and, at the same time, signals are applied from the FM detector 116through the bandpass filter 148 and the FM subcarrier detector 150 tothe speakers 134 and 136. Since the FM subcarrier detector 150demodulates the frequency modulated 4f_(H) second language subcarrier,the speakers 134 and 136 will reproduce the second language audiosignal. If switch 154 is closed but no second language subcarrier istransmitted, the mute control is inoperative and the stereo signal isautomatically reproduced.

The f_(H) pilot signal is also coupled from line 118 to the input of apilot detector 153. When the pilot detector 153 detects the presence ofan input f_(H) pilot signal it develops a signal on an output controlline 155 conditioning the stereo decoder 120 for suitable demodulatingthe stereo signals. In the absence of an f_(H) pilot signal, a controlsignal is developed on line 155 conditioning decoder 120 for operationin a monaural mode thereby preventing the possibility of decoding noisewhich might be present in the stereo subchannel.

FIG. 8 shows a circuit suitable for reproducing the transmitted ENGsignals. It will be appreciated that only a receiver operated by thebroadcasting station will include this circuit since the ENG signals areof no interest to the normal viewer. The receiver includes a receivingantenna 162 for intercepting the transmitted main audio RF carrier andfor coupling the received signal to the input of a tuner stage 164. Thetuner 164 converts the received RF audio carrier to a suitable IFfrequency which is amplified by an IF amplifier 166 and coupled to theinput of an FM detector 168. The FM detector 168 reconstructs thecomposite baseband signal at its output and the ENG component, i.e. thefrequency modulated 5.5f_(H) subcarrier, is separated therefrom by abandpass filter 170. The ENG component of the composite baseband signalis then coupled to an FM subcarrier detector 172 which demodulates the5.5f_(H) frequency modulated subcarrier. The demodulated subcarrier issubsequently coupled through a low-pass filter 174 to remove anyfrequency components above 3.4 KHz and through a 150 microsecondde-emphasis circuit 176 whereupon the ENG signal is reproduced by aspeaker 178.

FIG. 9 illustrates a receiver suitable for reproducing the transmittedtelemetry signals. As in the case of the ENG receiver of FIG. 8, only areceiver used for the broadcasting station will include this circuit.The receiver is substantially identical to the ENG receiver of FIG. 7especially in its front end where the antenna 162, the tuner 164, the IFamplifier 166 and the FM detector 168 are employed. However, a differentbandpass filter 190 is used in this case to separate the 6.5f_(H)frequency modulated telemetry subcarrier from the composite basebandsignal developed at the output of the FM detector 168. The frequencymodulated telemetry subcarrier signal is subsequently demodulated by anFM subcarrier detector 192 and coupled through a low-pass filter 194 forremoving any frequency components above 2.0 KHz. The filtered telemetrysignal may then be coupled to a suitable digital processing and readoutcircuit 198.

FIG. 10 illustrates the frequency spectrum of an alternate embodiment ofthe present invention. It has been found that the transmission standarddefined by the graph of FIG. 3 adversely affects the audio reproducingcharacteristics of certain monaural television receivers currently inthe field. In particular, it has been found that an objectionable amountof cross-talk may exist between the 4f_(H) subcarrier and the monauralaudio channel of these television receivers. This cross-talk may belargely avoided by modifying the transmission standard of FIG. 3 asillustrated in FIG. 10.

Referring to FIG. 10, it will be seen that the frequency spectrumillustrated therein is similar to that shown in FIG. 3 except that thesubcarrier for the second language signal has been displaced from 4f_(H)to 5f_(H) and that the channel defined by the 5.5f_(H) frequencymodulated subcarrier has been eliminated. This displacement of thesecond language subcarrier signal to 5f_(H) has been found to largelyeliminate the previously described cross-talk problem without at allimpacting the stereo transmission scheme of FIG. 3.

FIG. 11 illustrates a composite baseband signal source similar to thatof FIG. 2 but configured for producing the baseband signal defined bythe frequency spectrum of FIG. 10. Since the circuit of FIG. 11 isconfigured and operates in a manner nearly identical to the circuit ofFIG. 2, for purposes of brevity, a detailed discussion thereof will notbe repeated at this point. Suffice it to say that the two circuits areidentical except that, in the case of the circuit of FIG. 11, thesubcarrier and pilot generator 58 couples a subcarrier signal phaselocked to 5f_(H) rather than 4f_(H) to the second input of the FMmodulator 76 in the second language channel. In addition, the channeldefined by the 5.5f_(H) subcarrier has been eliminated and the channeldefined by the 6.5f_(H) subcarrier has been relabled as an auxiliarychannel which may be used to transmit either audio or digital typeinformation. When used to transmit digital information, the 6.5f_(H)channel preferably includes the 2 KH_(z) low pass filter 96, theremaining transmission parameters being as shown in Table 1 for theTelemety channel except that the main carrier deviation may be increasedto 3.0 KH_(z). When used to transmit audio signals, filter 96 ispreferably removed and replaced by a voice bandwidth filter from thechannel, the remaining transmission parameters being as shown in Table 1for the ENG channel except that the subcarrier and the main carrierdeviations may both be reduced to 3.0 KH_(z).

The television receiver circuits illustrated in FIGS. 4-7 may be used toprocess the signal produced by the transmitter of FIG. 1 including theaudio source shown in FIG. 11, the only difference being that thebandpass filter 148 of FIG. 7 must be configured for coupling the 5f_(H)second language signal to FM subcarrier detector 150 for processinginstead of the 4f_(H) subcarrier. The receiver of FIG. 9 may be used toprocess digital signals transmitted over the 6.5f_(H) channel of FIG. 11while a similar receiver including an audio output circuit may be usedto process audio signals transmitted over the channel.

What has thus been shown is a television audio transmission system,including transmitting and receiving apparatus, which systemcomprehensively exercises the available auido bandwidth with minimumdeleterious effects. In particular, the selection and use of thespecific subcarrier signals to produce the composite baseband signalfrequency modulating the main audio RF carrier is considered to produceadvantageous results heretofore unattained.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and therefor, the aim in the appended claims is tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What is claimed is:
 1. In a television signal transmitter of the typehaving a signal source defining a horizontal scanning line frequency andmeans for generating an audio transmission signal comprising a maincarrier signal frequency modulated by a composite modulation function,the improved apparatus for developing said composite modulation functioncomprising:means for developing first and second stereophonicallyrelated audio signals; means for developing a third audio signal; meansfor developing first and second subcarrier signals having frequenciesequal to two and five times said horizontal scanning line frequencyrespectively; means for developing a first modulation function componentcomprising the sum of said stereophonically related audio signals; meansfor developing a second modulation function component comprising adouble sideband suppressed carrier signal formed by amplitude modulatingsaid first subcarrier signal in accordance with the difference betweensaid stereophonically related audio signals; means for developing athird modulation function component comprising said second subcarriersignal frequency modulated in accordance with said third audio signal;and means for combining said first, second and third modulation functioncomponents for producing said composite modulation function.
 2. In atelevision signal transmitter of the type having a signal sourcedefining a horizontal scanning line frequency and means for generatingan audio transmission signal comprising a main carrier signal frequencymodulated by a composite modulation function, the improved apparatus fordeveloping said composite modulation function comprising:means fordeveloping first and second stereophonically related audio signals;means for developing a third audio signal; means for developing firstand second subcarrier signals having frequencies equal to two and fivetimes said horizontal scanning line frequency respectively; means fordeveloping a first modulation function component comprising the sum ofsaid stereophonically related audio signals; means for developing asecond modulation function component comprising a double sidebandsuppressed carrier signal formed by amplitude modulating said firstsubcarrier signal in accordance with the difference between saidstereophonically related audio signals; means for developing a thirdmodulation function component comprising said second subcarrier signalfrequency modulated in accordance with said third audio signal; meansfor developing a fourth modulation function component comprising a pilotsignal having a frequency equal to said horizontal scanning linefrequency; and means for combining said first, second, third and fourthmodulation function components for producing said composite modulationfunction.
 3. In a television signal transmitter of the type having asignal source defining a horizontal scanning line frequency and meansfor generating an audio transmission signal comprising a main carriersignal frequency modulated by a composite modulation function, theimproved apparatus for developing said composite modulation functioncomprising:means for developing first and second stereophonicallyrelated audio signals; means for developing a third auido signal; meansfor developing first and second subcarrier signals having frequenciesphase locked to two and five times said horizontal scanning linefrequency respectively; means for developing a first modulation functioncomponent comprising the sum of said stereophonically related audiosignals; means for developing a second modulation function componentcomprising a double sideband suppressed carrier signal formed byamplitude modulating said first subcarrier signal in accordance with thedifference between said stereophonically related audio signals; meansfor developing a third modulation function component comprising saidsecond subcarrier signal frequency modulated in accordance with saidthird audio signal; means for developing a fourth modulation functioncomponent comprising a pilot signal having a frequency phase locked tosaid horizontal scanning line frequency; and means for combining saidfirst, second, third and fourth modulation function components forproducing said composite modulation function.
 4. The improved apparatusaccording to claim 3 including means for developing a first informationsignal, means for developing a third subcarrier signal having afrequency equal to about 6.5 times said horizontal scanning linefrequency, means for developing a fifth modulation function componentcomprising said third subcarrier signal frequency modulated inaccordance with said first information signal and means for combiningsaid first, second, third, fourth and fifth modulation functioncomponents for producing said composite modulation function.
 5. In atelevision signal transmitter of the type having a video signaltransmitter including means developing a horizontal sync signal defininga horizontal scanning line frequency and an aural signal transmitterincluding means for frequency modulating a main carrier signal inaccordance with a composite modulation function, the improved apparatusfor developing said composite modulation function comprising:means fordeveloping first and second stereophonically related audio signals;means for developing a third audio signal; means for developing a firstinformation signal; means responsive to said horizontal sync signal forgenerating a pilot signal and first and second subcarrier signals havingfrequencies phase locked to the first, second and fifth harmonics ofsaid horizontal scanning line frequency respectively; means fordeveloping a third subcarrier signal having a frequency equal to about6.5 times said horizontal scanning line frequency; means for developinga first modulation function component comprising the sum of saidstereophonically related audio signals; means for developing a secondmodulation function component comprising a double sideband suppressedcarrier signal formed by amplitude modulating said first subcarriersignal in accordance with the difference between said stereophonicallyrelated audio signals; means for developing a third modulation functioncomponent comprising said second subcarrier signal frequency modulatedin accordance with said third audio signal; means for developing afourth modulation function component comprising said third subcarriersignal frequency modulated in accordance with said first informationsignal and; means for combining said pilot signal and said first,second, third, and fourth modulation function components for producingsaid composite modulation function.
 6. A television signal transmittercomprising:a video signal transmitter including means developing ahorizontal sync signal defining a horizontal scanning line frequency;means for generating an aural main carrier signal; means for generatingfirst and second stereophonically related audio signals; means forgenerating a third audio signal; means responsive to said horizontalsync signal for generating first and second subcarrier signals havingfrequencies phase locked to two and five times said horizontal scanningline frequency and for developing a pilot signal having a frequencyphase locked to said horizontal scanning line frequency; means fordeveloping a first modulation function component comprising the sum ofsaid stereophonically related audio signals;means for developing asecond modulation function component comprising a double sidebandsuppressed carrier signal formed by amplitude modulating said firstsubcarrier signal in accordance with the difference between saidstereophonically related audio signals; means for developing a thirdmodulation function component comprising said second subcarrier signalfrequency modulated in accordance with said third audio signal; meansfor developing a composite modulation function comprising said pilotsignal and said first, second and third modulation function components;and means for developing an audio transmission signal comprising saidmain carrier signal frequency modulated in accordance with saidcomposite modulation function.
 7. The signal transmitter according toclaim 6 including:means for developing a first information signal; meansfor generating a third subcarrier signal having frequency equal to about6.5 times said horizontal scanning line frequency; means for developinga fourth modulation function component comprising said third subcarriersignal frequency modulated in accordance with said first informationsignal and; means for developing a composite modulation functioncomprising said pilot signal and said first, second, third, and fourthmodulation function components.
 8. A receiver for a television signaltransmission system characterized by a transmitted aural signalcomprising a main carrier signal frequency modulated in accordance witha composite modulation function having a first component comprising thesum of first and second stereophonically related audio signals, a secondcomponent comprising a double sideband suppressed carrier signal formedby amplitude modulating a first subcarrier having a frequency 2f_(H) inaccordance with the difference between said stereophonically relatedaudio signals, a third component comprising a second subcarrier having afrequency 5f_(H) frequency modulated in accordance with a third audiosignal, and a fourth component comprising a pilot signal having afrequency f_(H), where f_(H) is the horizontal scanning line frequencyassociated with the horizontal sync signal of a transmitted televisionsignal, said receiver comprising:input means responsive to a transmittedtelevision signal for deriving said composite modulation function; meansresponsive to said derived composite modulation function forregenerating said first subcarrier signal in a form phase and frequencylocked to the second harmonic of said pilot signal; stereophonicdecoding means responsive to said derived composite modulation functionand to said regenerated subcarrier signal for developing a pair ofoutput audio signals corresponding to said first and secondstereophonically related audio signals; means responsive to said derivedcomposite modulation function for producing said third component; and FMdetector means responsive to said produced third component fordeveloping a third audio output signal corresponding to said third audiosignal.
 9. A receiver for a television signal transmission systemcharacterized by a transmitted aural signal comprising a main carriersignal frequency modulated in accordance with a composite modulationfunction having a first component comprising the sum of first and secondstereophonically related audio signals, a second component comprising adouble sideband suppressed carrier signal formed by amplitude modulatinga first subcarrier having a frequency 2f_(H) in accordance with thedifference between said stereophonically related audio signals and athird component comprising a second subcarrier having a frequency 5f_(H)frequency modulated in accordance with a third audio signal, where f_(H)is the horizontal scanning line frequency associated with the horizontalsync signal of a transmitted television signal, said receivercomprising:input means responsive to a transmitted television signal fordeveloping a first signal corresponding to said composite modulationfunction; a bandpass filter having a center frequency of 5f_(H) andresponsive to said first signal for developing a sound signalcorresponding to said third component of said composite modulationfunction; means for regenerating said first subcarrier signal;stereophonic decoding means responsive to said first signal and to saidregenerated subcarrier for developing a pair of output audio signalscorresponding to said first and second stereophonically related audiosignals; and an FM detector responsive to said second signal fordeveloping a third audio output signal corresponding to said third audiosignal.
 10. The receiver according to claim 9 wherein said compositemodulation function includes a fourth component comprising a pilotsignal having a frequency f_(H), said means for regenerating beingresponsive to said pilot signal and to said horizontal sync signal forphase and frequency locking said regenerated first subcarrier signal tothe second harmonic of said pilot signal.
 11. The receiver according toclaim 10 including first and second speaker means and switching meansselectively operable for coupling said first and second stereophonicallyrelated audio signals, respectively, to said first and second speakermeans or for coupling said third audio signal to said first and secondspeaker means.
 12. A receiver for a television signal transmissionsystem characterized by a transmitted aural signal comprising a maincarrier signal frequency modulated in accordance with a compositemodulation function having a first component comprising the sum of firstand second stereophonically related audio signals, a second componentcomprising a double sideband suppressed carrier signal formed byamplitude modulating a first subcarrier having a frequency 2f_(H) inaccordance with the difference between said stereophonically relatedaudio signals, a third component comprising a second subcarrier having afrequency 5f_(H) frequency modulated in accordance with a third audiosignal and a fourth component comprising a third subcarrier having afrequency approximately 6.5f_(H) frequency modulated in accordance witha first information signal where f_(H) is the horizontal scanning linefrequency defined by the horizontal sync signal of a transmittedtelevision signal, said receiver comprising:input means responsive to atransmitted television signal for developing a baseband signalcorresponding to said composite modulation function; and decoding meansresponsive to said baseband signal for developing therefrom said firstand second stereophonically related audio signals, said third audiosignal and said first information signal.
 13. A receiver for atelevision signal transmission system characterized by a transmittedaural signal comprising a main carrier signal frequency modulated inaccordance with a composite modulation function having a first componentcomprising the sum of first and second stereophonically related audiosignals, a second component comprising a double sideband suppressedcarrier signal formed by amplitude modulating a first subcarrier havinga frequency 2f_(H) in accordance with the difference between saidstereophonically related audio signals, a third component comprising asecond subcarrier having a frequency 5f_(H) frequency modulated inaccordance with a third audio signal and a fourth component comprising athird subcarrier having a frequency approximately 6.5f_(H) frequencymodulated in accordance with a first information signal, and a fifthcomponent comprising a pilot signal having a frequency f_(H), wheref_(H) is the horizontal scanning line frequency defined by thehorizontal sync signal of a transmitted television signal, said receivercomprising;input means responsive to a transmitted television signal fordeveloping a baseband signal corresponding to said composite modulationfunction; phase locked filter means responsive to said pilot signal andto said horizontal sync signal for regenerating said first subcarriersignal in a form phase and frequency locked to the second harmonic ofsaid pilot signal; and decoding means responsive to said baseband signaland to said regenerated subcarrier signal for developing therefrom saidfirst and second stereophonically related audio signals, said thirdaudio signal and said first information signal.
 14. A television signalaudio transmission system comprising: transmission means including asignal source defining a horizontal scanning line frequency f_(H)corresponding to the frequency of the horizontal sync signal of thevideo component of a transmitted television signal;means for developingfirst and second stereophonically related audio signals; means fordeveloping a third audio signal; means for developing first and secondsubcarrier signals having frequencies equal to 2f_(H) and 5f_(H)respectively; means for developing a pilot signal having a frequencyequal to f_(H) ; means for developing a first modulation functioncomponent comprising the sum of said stereophonically related audiosignals; means for developing a second modulation function componentcomprising a double sideband suppressed carrier signal formed byamplitude modulating said first subcarrier signal in accordance with thedifference between said stereophonically related audio signals; meansfor developing a third modulation function component comprising saidsecond subcarrier signal frequency modulated in accordance with saidthird audio signal; means for combining said pilot signal and saidfirst, second and third modulation function components for producing acomposite modulation function; means for generating an RF aural carriersignal; means for frequency modulating said aural carrier with saidcomposite modulation function; means for transmitting said modulatedaural carrier signal; receiver means comprising means for receiving saidtransmitted aural carrier signal and including input means for derivingsaid composite modulation function therefrom; means for regeneratingsaid first subcarrier signal; stereophonic decoding means responsive tosaid derived composite modulation function and to said regeneratedsubcarrier signal for developing a pair of output audio signalscorresponding to said first and second stereophonically related audiosignals; and an FM detector responsive to said derived compositemodulation function for developing a third audio output signalcorresponding to said third audio signal.
 15. The transmission systemaccording to claim 14 wherein said means for regenerating comprisesmeans responsive to said pilot signal and to said horizontal sync signalfor regenerating said first subcarrier signal in a form phase andfrequency locked to the second harmonic of said pilot signal.
 16. In atelevision signal transmitter of the type having a signal sourcedefining a horizontal scanning line frequency and means for generatingan audio transmission signal comprising a main carrier signal frequencymodulated by a composite modulation function, the improved method fordeveloping said composite modulation function comprising:generatingfirst and second stereophonically related audio signals; generating athird audio signal; generating first and second subcarrier signalshaving frequencies equal to two and five times said horizontal scanningline frequency respectively; generating a first modulation functioncomponent by forming the sum of said sterephonically related audiosignals; generating a second modulation function component by amplitudemodulating said first subcarrier signal in accordance with thedifference between said stereophonically related audio signals forforming a double sideband suppressed carrier signal; generating a thirdmodulation function component by frequency modulating said secondsubcarrier signal in accordance with said third audio signal; andcombining said first, second and third modulation function componentsfor producing said composite modulation function.
 17. In a televisionsignal transmitter of the type having a signal source defining ahorizontal scanning line frequency and means for generating an audiotransmission signal comprising a main carrier signal frequency modulatedby a composite modulation function, the improved method for developingsaid composite modulation function comprising:generating first andsecond stereophonically related audio signals; generating a third audiosignal; generating first and second subcarrier signals havingfrequencies equal to two and five times said horizontal scanning linefrequency respectively; generating a first modulation function componentby forming the sum of said stereophonically related audio signals;generating a second modulation function component by amplitudemodulating said first subcarrier signal in accordance with thedifference between said stereophonically related audio signals forforming a double sideband suppressed carrier signal; generating a thirdmodulation function component by frequency modulating said secondsubcarrier signal in accordance with said third audio signal; generatinga fourth modulation function component comprising a pilot signal havinga frequency equal to said horizontal scanning line frequency; andcombining said first, second, third and fourth modulation functioncomponents for producing said composite modulation function.
 18. Themethod of developing a composite modulation function according to claim17 wherein said pilot signal, said first subcarrier signal and secondsubcarrier signal are phase locked to the first, second and fourthharmonics respectively of said horizontal scanning line frequency. 19.In a television signal transmitter of the type having a video signaltransmitter including means developing a horizontal sync signal defininga horizontal scanning line frequency and an aural signal transmitterincluding means for frequency modulating a main carrier signal inaccordance with a composite modulation function, the improved method ofdeveloping said composite modulation function comprising:generatingfirst and second stereophonically related audio signals; generating athird audio signal; generating first and second information signals;generating a pilot signal and first and second subcarrier signals havingfrequencies equal to one, two and five times said horizontal scanningfrequency respectively; generating a third subcarrier signal having afrequency approximately equal to 6.5 times said horizontal scanning linefrequency; generating a first modulation function component comprisingthe sum of said stereophonically related audio signals; generating asecond modulation function component comprising a double sidebandsuppressed carrier signal formed by amplitude modulating said firstsubcarrier signal in accordance with the difference between saidstereophonically related audio signals; generating a third modulationfunction component comprising said second subcarrier signal frequencymodulated in accordance with said third audio signal; generating afourth modulation function component comprising said third subcarriersignal frequency modulated in accordance with said first informationsignal; and combining said pilot signal and said first, second, third,and fourth modulation function components for producing said compositemodulation function.
 20. The method of developing a composite modulationfunction according to claim 19 including the step of phase locking saidpilot signal and said first and second subcarrier signals to the first,second and fifth harmonics respectively of said horizontal sync signal.21. The method of implementing a television signal audio transmissionsystem comprising:generating first and second stereophonically relatedaudio signals; generating a third audio signal; generating first andsecond subcarrier signals having frequencies equal to 2f_(H) and 5f_(H)respectively, where f_(H) is equal to the frequency of the horizontalsync signal of the video component of a transmitted television signal;generating a pilot signal having a frequency equal to f_(H) : generatingfirst modulation function component comprising the sum of saidstereophonically related audio signals; generating a second modulationfunction component comprising a double sideband suppressed carriersignal formed by amplitude modulating said first subcarrier signal inaccordance with the difference between said stereophonically relatedaudio signals; generating a third modulation function componentcomprising said second subcarrier signal frequency modulated inaccordance with said third audio signal; combining said pilot signal andsaid first, second and third modulation function components forproducing a composite modulation function; generating an RF auralcarrier signal; frequency modulating said aural carrier with saidcomposite modulation function; transmitting said modulated aural carriersignal; receiving said transmitted aural carrier signal and derivingsaid composite modulation function therefrom; regenerating said firstsubcarrier signal; using said regenerating subcarrier signal fordecoding said composite modulation function for developing a pair ofoutput audio signals corresponding to said first and secondstereophonically related audio signal; and detecting said derivedcomposite modulation function for developing a third audio output signalcorresponding to said third audio signal.
 22. The method according toclaim 21 wherein said pilot signal and said first and second subcarriersignals are phase locked to the first, second and fifth harmonicsrespectively of said horizontal sync signal.